1. Field of the Invention
This invention relates to methods of estimating the quantity of methane generated through manipulation of a reservoir in a sub-surface environment. The invention also relates to methods of differentiating the newly generated methane from pre-existing methane in a sub-surface reservoir.
2. Background
Methane, CH4, is an environmentally important greenhouse gas and an economically important fuel. Methane is produced in nature by four principle processes, biogenesis (as the end product of microbial metabolism), thermogenesis (chemical degradation of organic material at elevated temperature and pressure), geogenesis (as the result of interaction between geologic fluids with chemically reduced rocks), and ignigenesis (as a byproduct of combustion). Of the total 1.2 to 1.4×1015 g of methane produced annually, the majority of this methane (likely greater than 85%) is produced biogenically.
Biogenic methane production, also referred to as methanogenesis, occurs at all temperatures between freezing and boiling. The majority of methane currently released to the atmosphere is produced near the surface, at temperatures between 0 and 50° C. Abundant CH4 is also produced in environments with elevated temperatures (moderately thermal environments, defined here as having temperatures from around 50 to 130° C.), which include geothermal springs, hydrothermal vents, and waste digestors.
The most important of these moderately thermal methanogenic environments are deeply buried sediments, which are heated from below by the geothermal gradient (comprising much of the “deep biosphere”). Methane produced in sub-surface environments generally migrates along the concentration gradient toward the ocean and atmosphere, often being physically or chemically trapped in the sub-surface environment. The trapping of methane allows for the buildup of a large reservoir, which acts as a major source of methane. Thus, there is a current movement in the field towards enhanced recovery of methane from reservoirs in sub-surface environments.
Several companies and scientific groups have been actively developing processes that manipulate sub-surface environments to facilitate methanogenesis or the biological production of methane. However, there is no known art dealing with methods designed specifically to assess and quantify the “new methane” generated through the facilitated methanogenesis. Furthermore, there is no known art related to methods of differentiating the newly generated methane from the methane pre-existing in the reservoir. One current approach would be to monitor the rate of total methane removal from the reservoir before and after augmentation, but many factors control this rate and attribution to any augmentation process is purely inference.
Differentiating between newly generated methane and pre-existing methane is important for companies in determining and comparing the efficacy of various methanogenesis facilitation processes to estimate the success and profitability of augmentation technologies. Distinguishing the newly generated methane is also important for the natural gas mining companies and their partners in terms of profit sharing and royalties.
Thus, there is a need for a method of estimating and quantifying methane generated through manipulation, such as augmentation or biostimulation, of a reservoir. There is also a need for a method of distinguishing newly generated methane from pre-existing methane in the reservoir. The present invention satisfies this need.